(TNS) -- As fast-moving fires invaded neighborhoods across Northern California this week, residents in Napa and Sonoma counties said they were alerted to the approaching disaster by frantic shouts from neighbors, honking horns, blaring smoke alarms and even the noise of an American flag whipping in the intense winds.

But it’s becoming increasingly clear that at least some residents did not receive warnings on their cellphones similar to an Amber Alert. The so-called Wireless Emergency Alert sends loud, screeching alarms or vibrations to all cellphones in a geographic area unless a user specifically opts out.

On Wednesday, officials faced questions about why authorities could not reach more people as the fires barreled toward homes late Sunday night and early Monday morning.

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Sonoma County Sheriff Rob Giordano said Wednesday that the county sent out warnings through its SoCoAlert service and Nixle, both systems that require residents to register in advance in order to receive messages. The county also sent out reverse 911 calls to landlines in unincorporated areas. Santa Rosa, where block after block of suburban homes was destroyed, sent out alerts through SoCoAlert, Nixle and on social media.

Sonoma County is among dozens of California jurisdictions that applied forand received authority from the federal government to issue Wireless Emergency Alerts. It’s unclear whether the county tried to use the system this week and, if so, why it didn’t reach some people.

Napa County issued alerts through Nixle, but officials said some residents had trouble receiving the warnings.

The death toll from the fires rose Wednesday to at least 23, with some victims simply unable to outrun the flames. An estimated 3,500 homes, businesses and other structures were burned.

In the devastated Coffey Park neighborhood of Santa Rosa, some residents of scorched homes said they were surprised they didn’t get an alert on their phones.

Michael Desmond, 59, a retired homeland security investigator, said he was lying in bed Sunday night skimming news stories on his iPad when he heard a commotion outside. Finally, he heard what a firefighter was saying: “Firestorm. Get out of here now! Take nothing! Just go!”

“So I got my dog. I got my wallet. Got my keys. And left,” he said Wednesday, as he walked down the street of his neighborhood carrying a charred mailbox, one of the few things he was able to salvage from his home destroyed by wildfire.

“I think they were totally unprepared for this,” he said.

A few blocks away, high school teacher Anna Solano, 50, said she also received no phone warning.

Solano, who on Wednesday sifted through the ashes of her home looking for keys to equipment lockers and classrooms, had smelled smoke earlier Sunday evening but thought there was just a house fire in the area. About 2:30 a.m. Monday, a man knocked on her door and kept banging, waking up Solano’s dog, who eventually woke her up.

“That gentleman saved our lives. A stranger,” she said. “We saw the fire coming. We left here in five minutes.”

The fire — one of the most destructive in California history — moved through northern Santa Rosa swiftly, with winds clocking 50 mph carrying embers that ignited numerous spot fires, burning down entire neighborhoods.

“The fire came through the night. It was rapidly moving,” said Mark Ghilarducci, director of the California Governor’s Office of Emergency Services. “Some people were awakened while the fire was actually on their doorstep.”

Sonoma County officials said it will take time to determine the reach of the alerts they tried to issue.

“I don’t know how effective that was,” said Giordano, the Sonoma County sheriff. “It’s going to take a long time until we understand that.”

The Wireless Emergency Alert system was rolled out in 2012, and California used it to send an Amber Alert for the first time in 2013. The alerts are transmitted on an exclusive frequency that can reach many people at the same time, and Amber Alerts — which notify the public of the case of an abducted child — have proven effective.

Alerts like these have been used to warn New Yorkers about the approach of Hurricane Sandy and tell the people of Moore, Okla., about the arrival of a massive tornado.

But some local jurisdictions don’t use them — or don’t know how.

This year, San Jose officials were roundly chastised for failing to warn the public about destructive floodwaters before they overflowed through densely populated neighborhoods along Coyote Creek amid the winter’s heavy rains.

In July, a withering report concluded that in San Jose, “there was a general lack of institutional knowledge” on how to broadcast alerts on the Wireless Emergency Alert system. San Jose itself at the time was not set up to issue such alerts on its own. Santa Clara County did have the ability to do so, but no one from the city asked the county to release an alert on its behalf.

For local authorities to use the federal system, municipalities need to apply to the Federal Emergency Management Agency to become an alerting authority. The city of Los Angeles, Orange County, San Francisco and Sacramento County are among the jurisdictions that have registered to use the wireless alert system.

Napa County is not listed. Heather Ruiz, a spokeswoman for the Napa County Office of Emergency Services, said her county has not been using the Wireless Emergency Alert system and was not sure if they had the ability to do so. Instead, they issue alerts through Nixle.

Mark Eggan, Napa County Sheriff’s Office information technology chief, said 1,500 people responded to a Nixle alert Sunday night by clicking on a link to the department’s web server, causing it to crash. During the server’s crash, people could read the brief message on their phones, but the link to get further information did not work. Eggan said the system had never been taxed like that before.

This week, Napa County officials said it’s possible alerts were hampered by fire damage to cellphone towers. The fragility of the cellphone tower network — highlighted by natural disasters in Texas, Florida and Puerto Rico — caused the chairman of the Federal Communications Commission, Ajit Pai, to put the spotlight on technology in cellphones that can be used to receive alerts through a chip that can receive FM radio signals, which can work even when cellphone towers are powerless or destroyed.

Though other cellphone manufacturers equip their phones with FM chips, Apple says its most recent models, the iPhone 7 and 8, do not have them.

“It is time for Apple to step up to the plate and put the safety of the American people first,” Pai said in a statement released last month.

Pai said he has long urged cellphone manufacturers that had turned off FM chips on their cellphones to reactivate them so that people can use them to “get vital access to life-saving information.” He applauded companies that have done so, and singled out Apple as “the one major phone manufacturer that has resisted doing so.”

In a statement, Apple said the company “cares deeply about the safety of our users” and noted that users can dial emergency services and receive Amber Alerts and emergency weather notifications. The company did not respond to questions about whether the company would install FM chips in future models of the iPhone.

Jurisdictions in California with authority to issue Wireless Emergency Alerts, which are transmitted through FEMA’s Integrated Public Alert and Warning System (IPAWS), as of Aug. 8:

Alameda County Operational Area

Butte County

California Governor’s Office of Emergency Services

California Highway Patrol

City of Lancaster

City of Los Angeles

City of Monterey Park

City of Moreno Valley Emergency Operations Center

City of Oakland

City of Rancho Cucamonga

City of San Leandro

City of Tehachapi

City of Torrance Police Department

Contra Costa County Office of the Sheriff

County of Sacramento

County of Tulare

County of Tuolumne

Fresno County Sheriff-Coroner’s Office

Lake County Sheriff’s Office of Emergency Services

Madera County Sheriff's Department

Marin County Sheriff's Office of Emergency Services

Mendocino County Sheriff's Office

Merced County Office of Emergency Services

Mono County Sheriff's Office

Monterey County

Northern California Regional Intelligence Center

Orange County

Placer County Office of Emergency Services

Riverside & San Bernardino Counties (LECC)

San Diego County Office of Emergency Services

San Francisco Department of Emergency Management

San Francisco International Airport

San Joaquin County Office of Emergency Services

San Luis Obispo County Office of Emergency Services

Santa Barbara County

Santa Clara County Office of Emergency Services

Santa Cruz Regional 9-1-1

Shasta Area Safety Communications Agency (SHASCOM)

Siskiyou County

Solano County Sheriff's Office of Emergency Services

Sonoma County Fire and Emergency Services Department

Stanislaus County Office of Emergency Services

Tehama County Sheriff's Office

Town of Truckee Police Department

Ventura County Sheriff's Office - Office of Emergency Services

Yolo County

Jurisdictions in California in the process of obtaining the ability to issue the system used to issue Wireless Emergency Alerts, as of Aug. 8: